PEPC is useful in the measurement of bicarbonate in biological samples. When this enzyme is linked to malate dehydrogenase, the concentration of bicarbonate is directly proportional to the consumption of oxaloacetate and NADH, as follows (MDH=malate dehydrogenase; PEP phosphoenolpyruvate): ##STR1##
The most popular commercial sources of PEPC are Zea maize and wheat germ. From both sources, the PEPC has poor intrinsic stability (i.e. in the absence of stabiliser), there are inconsistencies in the raw material, and batch-to-batch variation occurs in the quality of the final product. Further the PEPC may be obtained together with PEP-degrading enzymes which may affect the stability of the assay kit.
It would be desirable if PEPC could be obtained from more consistent raw material, and that there should be no seasonal limitations on raw materials. Further, there would desirably be simpler purification, less significant contaminating enzymes, more liquid stability, and increased activity. Commercially-available PEPC usually has a specific activity of about 5 units/mg, although activities of 20-22 units/mg protein have been claimed.